Network Transfer Mechanisms
The proliferation and expansion of computer information systems coincides with an increase in network use. More and more often, people are using computer networks and software to transfer large amounts of data. The increased communications over the Internet has resulted in an explosion of data transfers and connections in various contexts.
There are three general manners of transferring content across a network: unicast, multicast, and broadcast. Unicast transmissions are sent from a single originator to a single receiving entity; they are point-to-point. An example of a unicast transmission is the simple downloading of a file over the Internet via TCP/IP packets. If there are multiple receivers wishing to obtain content across a unicast network, then each needs to establish its own data connection to an originator. Broadcast and multicast are methods for transmitting datagrams from a single source to several destinations (point-to-multipoint). Generally, multicast transmissions are sent to specific groups, whereas broadcast transmissions are sent to everyone in range. Both broadcast and multicast mechanisms conserve network bandwidth by sending a single stream of data to be obtained by multiple receivers. The universal mobile telecommunications system (UMTS) network, which was originally a broadcast network designed for video or audio broadcasting (e.g., digital video broadcasting—terrestrial (DVB-T) and digital audio broadcasting (DAB)), is able to provide both multicast and broadcast services. As the broadcast system was designed to distribute popular content to a large group or audience, the broadcast system is characterized as having a high bandwidth and wide cell coverage area. As such, it is suitable for distributing multimedia multicast/broadcast content that is targeted to a large group of users. To date, 3G release-4 and release-99 define two services with respect to point-to-multipoint communication—a cell broadcast service and an IP-multicast service. A cell broadcast service allows low bit-rate data to be transmitted to all subscribers in a set of given cells over a shared broadcast channel. An IP-multicast service allows mobile subscribers to receive multicast traffic. Another point-to-multipoint communication method, the multimedia broadcast/multicast service (MBMS), allows links to be used for distributing popular content to groups of users simultaneously. The use of a point-to-multipoint link saves radio spectrum resources if there are many users accessing the same information in a given cell.
In some systems like wideband code division multiple access (WCDMA), the transmission power limits the capacity. In such instances, using a common channel may consume more bandwidth resources than using multiple point-to-point links; for example, in case where there are only few users (e.g. less than 4) in the cell who shares the information.